Label film with improved adhesion

ABSTRACT

The invention relates to the use of a biaxially oriented polyolefin film as a label film. The inventive film consists of a base layer and at least one cover layer. Said cover layer contains as the main component a copolymer or terpolymer consisting of one alkene and unsaturated carboxylic acids or the esters thereof and low amounts of an additive. The cover layer is characterized by excellent and divers adhesion to various polymer materials from which containers are formed. It is no longer necessary to apply adhesives, primers, coatings etc. in a separate step after production of the film.

The invention relates to the use of a biaxially oriented thermoplasticfilm for labels having improved adhesion to various materials,specification to the labels themselves, and to a process for theproduction of the labels.

BACKGROUND OF THE INVENTION

Foods and other goods are frequently packed in rigid-walled containerswhich, as early as during production, are provided with a label by the“in-mould labelling” or “IML method”. In this method, a label is laid,usually by a robot, in the open mould in such a way that the printed(out)side of the label is in contact with the mould wall, while theunprinted (inside) faces the container to be shaped. Flat, fold-freelying of the label in the mould is achieved, for example, by means of avacuum applied to fine air-removal perforations, with the perforationsbeing substantially sealed by the label. Alternatively, electrostaticforces between the electrostatically charged label and the earthed mouldensure flat lying of the label.

The advantage of the IML method is that the print quality of theseparately produced labels is significantly better than direct printingof the containers. Application of the label during shaping of thecontainer is inexpensive and effective. There is no need for adhesives,coated backing films or papers and it is therefore not necessary todispose of waste and residues. The in-mould labelling method can becombined with various container production processes. Variants of theIML method have been proposed or already developed for, for example,injection moulding, thin-wall injection moulding, blow moulding andthermoforming and the injection stretch blow moulding of containers.

Furthermore, methods for labelling containers after their production orafter their filling are known, such as, for example, wrap-aroundlabelling, patch labelling, self-adhesive labels and thermolabelling.

Thermolabelling covers all methods in which a label is applied to acontainer under the action of heat. For example, the pre-shapedcontainer can be heated in a suitable process and the label pressed ontothe container wall by means of pressure or with the aid of brushes orrolls in such a way that it is subsequently firmly bonded to thecontainer.

In both in-mould labelling and thermolabelling, bubble-free applicationof the label is an important and at the same time problematicrequirement. In order to achieve this, the inside surface of the labelfilm, i.e. the one facing the container, is frequently structured orroughened to simplify exit of air from the gap between label andcontainer wall.

In the case of simple label shapes, the label is usually supplied inroll form and cut to size on the machine in which the container isshaped (cut in place). This method is particularly appropriate in thecase of simple, for example rectangular, label shapes, as are used, inparticular, in wrap-around labelling (WAL) and patch labelling ofessentially cylindrical containers and bottles.

In the case of more complex outlines, the label is frequently cut tosize in advance, stacked in magazines, later removed from the stack atthe labelling machine and laid in the mould (cut & stack method). Thelabels here are firstly printed, for example, by the so-called sheetoffset method or other suitable methods and cut to their final shapedirectly after the printing process. Both the unprinted and the printedsheets and labels must be readily processable in the individual processsteps of sheet cutting, printing, label cutting and feeding tolabelling. The sheet and the label are stacked and unstacked. In theprocess, the films must slide easily against one another and they mustnot become electrostatically charged. Besides providing the label filmwith lubricants and antistatics, corresponding structuring of the filmsurface is therefore necessary.

For the production of the containers, use is made of various materials,such as, for example, polypropylene (PP), high- or low-densitypolyethylene (HD-PE or LD-PE or LLD-PE, polystyrene (PS), polyvinylchloride (PVC), polyethylene terephthalate PET; polycarbonate (PC) andin individual cases also mixtures of such polymers. This gives rise tovarious requirements of the label materials with respect to strength,extensibility, rigidity, gloss/mattness and adhesion to the containerwall. For cost reasons, biaxially oriented polypropylene films (BOPPfilms) are preferably employed, these applications currently beingrestricted to containers made from polypropylene and polyethylene.

The conventional BOPP labels adhere, even at elevated temperatures,poorly to the other container materials mentioned. It is not possible toapply labels made from BOPP film to containers made from PET, PS, PC orPVC by means of in-mould or thermolabelling methods. In particular, ithas hitherto not been possible to use BOPP films in theinjection-moulding IML method on polystyrene. It has been just asunsuccessful to employ label films made from BOPP films in thethermolabelling method on PET bottles. Here, corresponding adhesiveshave to be applied for attaching the label. In spite of extensiveattempts to combine various container materials and various labelmaterials with the diverse known labelling methods, the choice ofsuccessful combinations remains very restricted. The direct use of BOPPfilms in the IML or thermolabelling method for the labelling ofcontainers which do not consist of PP or PE has hitherto notbeen-possible. For the adhesion of BOPP labels to PS, PET, PC, PVC,etc., adhesives, coatings, lacquers or similar aids are necessary, itbeing necessary to apply these subsequently, i.e. after production ofthe film, in an additionally processing step. This firstly makes thelabel more expensive and sometimes has a disadvantageous effect on theother service properties.

British Application GB 2 223 446 discloses a BOPP film which consists ofat least two layers, with the comparatively thinner layer consisting ofa blend of a material which has low seal seam strength to PVDC and amaterial which consists of a copolymer of an alkene and an unsaturatedmonobasic acid or ester thereof. In preferred embodiments, suitablematerials having low seal seam strength to PVDC are high- andlow-density polyethylenes, and suitable copolymers are those of ethylenewith acrylic acid esters, where, in particularly preferred embodiments,these copolymers can comprise unsaturated dibasic acids or anhydridesthereof, such as, for example, maleic anhydride, as further monomers.Corresponding copolymers and terpolymers have been described in EP 0 065898.

On repetition of British Application GB 2 223 446, it was observed thatthe process described therein results, on use of the formulationsindicated therein, in considerable deposits on the heating andstretching rolls of the longitudinal stretching unit of a sequentialBOPP machine which are unacceptable for industrial practice. Variationswithin the limits of the disclosed teaching brought about no advantageor only a slight advantage with respect to the amount and speed of theroll coating built up, or other service properties were adverselyaffected.

The object of the present invention was to provide a biaxially orientedpolyolefin film which is inexpensive and can be employed in a diversemanner as label film. The film should, in particular, be applicable bythe IML or thermolabelling method to containers made from variousmaterials, such as, for example, PP, PE PET, PS, PC, PVC, etc. andshould have good adhesion. It is of course necessary that the film canbe produced without the formation of deposits on the rolls of thelongitudinal stretching unit. In addition, the other important serviceproperties and the appearance of the film, or of the label producedtherefrom, should not be adversely affected. In particular, the filmshould be printable on one side and should be readily stackable anddestackable in the processing process.

BRIEF DESCRIPTION OF THE INVENTION

This object is achieved by the method of making a label film, whichmethod comprises converting a multilayered biaxially oriented polyolefinfilm comprising a base layer and at least one inner top layer, wherethis inner top layer comprises at least 70% by weight of a copolymer orterpolymer I built up at least from an olefin and an unsaturatedcarboxylic acid or esters thereof or anhydrides thereof, and not morethan 30% by weight of an additive, wherein the data in % by weight arein each case based on the weight of the inner top layer into a labelfilm. The dependant claims indicate preferred embodiments of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Within the scope of the present invention, it has been found,surprisingly, that the inner top layer comprising the said copolymersand/or terpolymers I has excellent adhesion as a label to a very widevariety of polymer materials from which containers are usually shaped.It is thus possible, for the first time, to make available a materialwhich, surprisingly, can be employed equally successfully for thelabelling of containers made from PP or PE or PVC or PET or PC or PS bythe thermolabelling or in-mould method. It has been found here that asmall amount of an additive in the inner top layer comprising copolymeror terpolymer I effectively prevents roll deposits during production ofthe film and at the same time the desired good and diverse adhesionproperties of the film are not impaired on use as an IML orthermolabelling label. In particular, it has been observed that a toplayer built up only from the copolymer or terpolymer I sticks to therolls or forms deposits during production of the film in such a way thathandling of the material in the film production process is virtuallyimpossible.

Surprisingly, the film according to the invention, on use thereof aslabel in the in-mould and thermolabelling method, exhibits excellentadhesion properties, not only to containers made from PP and PE. Thefilm can also be applied extremely well as a label to containers madefrom PS, PVC, PC and PET without additionally adhesives, lacquers,coatings or other auxiliaries being necessary. On use according to theinvention as label film in the IML or thermolabelling method, very goodadhesion between label and container is found. Thus, a material whichcan be employed in a hitherto impossible breadth for a very wide varietyof container materials is made available for the first time. This alsohas considerable logistical advantages.

Owing to these particular adhesion properties, this film can be used notonly for the labelling of containers made from PP, PE, PS, PVC, PC andPET, but also in a specific application as lid film for containers madefrom PP, PE, PS, PVC, PC and PET. Suitable containers are containers ofany desired shape, such as, for example, pots, dishes, casting parts,etc. It has been found that the inner top layer also has very goodadhesion as a lid and seals the containers well and thus reliablyprotects them against contamination. At the same time, the film can bepeeled off from the container without leaving a residue when the packcontents are to be removed. Known lid films in accordance with the priorart, after peeling-off from the container, frequently leave shred-likewhite skins at the edge or in the heat-sealing or embossing region ofthe container to which the film has been welded. These film residues,which then remain adhering to the container edge, may interfere withremoval of the pack contents, cannot readily be identified by theconsumer and are therefore unacceptable. As a further advantage, it hasbeen found that the lid film can be applied at temperatures of <100° C.,preferably from 70 to <100° C., and the good adhesion is alreadyachieved at these temperatures. The container edge and/or theintermediate webs thus remain dimensionally stable.

It has furthermore been found that the film with its inner top layeralso has excellent adhesion properties to surfaces made from paper,wood, metal, for example aluminium or tinplate. Owing to these adhesionproperties, the film can advantageously be employed for furtherapplications.

The film can be employed for lamination to other sheet-like substrateswithout an adhesive having to be applied for adhesion of the label tothe substrate. For example, the film can be laminated directly, withexcellent results, with its inner surface to paper, aluminium and otherthermoplastic films. Furthermore, the film exhibits on the surface ofthe inner top layer increased adhesion to cold-sealing adhesives,printing inks and diverse coatings applied after production of the film.In a further application, the film exhibits improved adhesion in thecase of metallization by means of vacuum vapour deposition.

The essential factors for these good adhesion properties is thestructure and composition of the inner top layer of the film. This innertop layer faces the container during labelling and forms the bondbetween container and label. For corresponding applications as lid film,the inner top layer faces the container during application of the lidand forms the bond between lid film and container.

For the purposes of the present invention, the inner top layer is thetop layer which faces the container during labelling and forms the bondbetween the container and the label during labelling. The structure andcomposition of the inner top layer are the essential factors for thegood and diverse adhesion properties of the label. It has been foundthat the surface of the inner top layer has increased surface roughness,which simplifies destacking during the labelling process and supportsbubble-free application. Surprisingly, the good and diverse adhesionproperties are not impaired by this surface roughness.

The inner top layer comprises, as constituents which are essential tothe invention, a copolymer or terpolymer I comprising an olefin and anunsaturated carboxylic acids or esters thereof or anhydrides thereof andan additive. If desired, the inner top layer additionally comprisesantiblocking agents. In general, the inner top layer comprises at least70% by weight, preferably from 80 to 99.5% by weight, in particular from85 to 99% by weight, of the copolymer or terpolymer I, and at most 30%by weight, preferably from 0.5 to 20% by weight, in particular from 1 to15% by weight, of the additive, in each case based on the weight of theinner top layer.

Suitable copolymers or terpolymers I are built up from olefins andunsaturated carboxylic acids or esters thereof or anhydrides thereof asmonomers. Olefins are, for example, ethylene, propylene or 1-butene, ifdesired also higher homologues, such as, for example, hexene or octene.Unsaturated carboxylic acids include unsaturated mono- and dicarboxylicacids and esters or anhydrides thereof. Preferred unsaturated carboxylicacids are acrylic acid or methacrylic acid and esters thereof. Inprinciple, the copolymer or terpolymer I can be built up from differentolefins and different unsaturated carboxylic acids or esters/anhydridesthereof. Copolymers I comprising ethylene and acrylic acid ester ormethacrylic acid ester are particularly advantageous.

Terpolymers I are generally built up from three different monomers (a),(b) and (c). The monomers (a) include the above-mentioned olefins, themonomers (b) are unsaturated carboxylic acids or esters thereof, andmonomers (c) are carboxylic acid esters or carboxylic acid anhydrideswhich are different from (b). Preferred monomer (c) are unsaturatedmonocarboxylic acid esters, for example glycidyl methacrylate, orunsaturated dicarboxylic acids or an anhydride thereof, such as, forexample maleic acid or maleic anhydride. Terpolymers comprising (a)ethylene, (b) acrylic acid or methacrylic acid or esters thereof and (c)glycidyl methacrylate or maleic anhydride are particularly advantageous.

The esters of the unsaturated carboxylic acids described are derivedfrom one or more lower alcohols. Methyl, ethyl, n-propyl, i-propyl,n-butyl, i-butyl, sec-butyl or tert-butyl esters, for example, aresuitable.

The composition of the copolymers or terpolymers I comprising therespective monomers can vary within the limits described below.Copolymers I generally comprise at least 60% by weight, preferably from70 to 97% by weight, of olefin, preferably ethylene, and at most 40% byweight, preferably from 3 to 30% by weight, of unsaturated carboxylicacids or esters thereof, preferably acrylic acid or methacrylic acid oresters thereof. Terpolymers I generally comprise

-   (a) from 65 to 96% by weight, preferably from 72 to 93% by weight,    of olefin, preferably ethylene, and-   (b) from 3 to 34% by weight, preferably from 5 to 26% by weight, of    unsaturated carboxylic acids or esters thereof, preferably acrylic    acid or methacrylic acid or esters thereof, and-   (c) from 1 to 10% by weight, preferably from 2 to 8% by weight, of    unsaturated mono- or dicarboxylic acids or esters thereof or an    anhydride thereof which are different from (b), preferably maleic    anhydride or glycidyl methacrylate.

The above-described copolymers or terpolymers I of the inner top layergenerally have a melting point of from 40 to 120° C., preferably from 60to 100° C. The Vicat point (in accordance with DIN 53460) is preferablyin the range from 30 to 90° C. The melt flow index is generally from 0.1to 20 g/10 min (190° C., 21.6 N), preferably from 0.1 to 15 g/10 min.

As a further essential component, the inner top layer comprises anadditive in an amount of from 1 to 30% by weight, based on the weight ofthe inner top layer, preferably a wax, preferably polyethylene waxes, orparaffins. Polyethylene waxes are low-molecular-weight polymers whichare essentially built up from ethylene units and are partly or highlycrystalline. The polymer chains from the ethylene units are extendedmolecules, which may be branched, with relatively short side chainspredominating. In general, polyethylene waxes are prepared by directpolymerisation of ethylene, if desired with use of regulators, or bydepolymerisation of polyethylenes of relatively high molecular weights.The polyethylene waxes preferably have a mean molecular weight Mn(number average) of from 200 to 5000, preferably from 400 to 2000,particularly preferably from 400 to 1000, and preferably have amolecular weight distribution (poly-dispersity) Mw/Mn of less than 3,preferably from 1 to 2. The melting point is generally in the range from70 to 150° C., preferably from 80 to 100° C.

Paraffins include macrocrystalline paraffins (paraffin waxes) andmicrocrystalline paraffins (microwaxes). Macrocrystalline paraffins areobtained from vacuum distillate fractions in the processing oflubricating oils. Microcrystalline paraffins originate from the residuesof vacuum distillation and the sediments of paraffinic crude oils(deposition paraffins). Macrocrystalline paraffins consist predominantlyof n-paraffins which additionally contain isoparaffins, naphthenes andalkylaromatic compounds, depending on the degree of refining.Microcrystalline paraffins consist of a mixture of hydrocarbons whichare predominantly solid at room temperature. In contrast to thesituation in macrocrystalline paraffins, isoparaffins and naphthenicparaffins predominate. Microcrystalline paraffins are distinguished bythe presence of crystallisation-inhibiting, highly branched isoparaffinsand naphthenes. For the purposes of the invention, paraffins having amelting point of from 60 to 100° C., preferably from 60 to 85° C., areparticularly suitable.

In a further embodiment, the inner top layer may comprise, as additive,one or more other component which prevents or prevent deposits duringfilm production in the same way as the wax. The proportion of additivesof this type is generally between 2 and 30% by weight, preferably from 3to 20% by weight, in particular from 3 to 10% by weight, with theproportion of copolymer or terpolymer I in the composition of the innertop layer being reduced correspondingly. Suitable additives of this typeare polyolefins, polystyrene, polyesters, polyamides and hydrocarbonresins.

Particularly suitable polyolefins are those with no carboxylic acidmonomers. Particular preference is given to polyolefins which aredescribed below as copolymers and terpolymers II in connection with theouter top layer, in particular propylene polymers or polyethylenes.Suitable polyethylenes are both linear and branched polyethylenes, forexample MDPE, VLDPE, LLDPE, LDPE or HDPE.

Suitable hydrocarbon resins are natural or synthetic resins having asoftening point of 80–180° C., such as, for example, hydrocarbon resins,ketone resins, colophony, dammar resins, polyamide resins and aliphaticand aromatic hydrocarbon resins.

In in-mould labelling or thermolabelling, it is particularly desirablefor bubble-free application of the label that the inner surface of thelabel film is appropriately structured in order to simplify exit of theair from the gap between label and container wall. It has been foundthat blending of the copolymers and terpolymers I with polyethylenes asadditive contributes to a rough surface of the inner top layer, whichhas a favourable effect on “air removal” during labelling. PE-containingcompositions of this type for the inner top layer are thereforeparticularly advantageous with respect to the appearance of the appliedlabel.

If desired, the inner top layer may also comprise mixtures of theabove-mentioned additives, particular preference being given to mixturesof wax and polyethylene. Combinations of 1–10% by weight of wax and1–10% by weight of polyolefin, in particular copolymers II orpolyethylenes (in each case based on the weight of the top layer), areparticularly advantageous here with respect to deposits during filmproduction without reducing the adhesion properties of the label.

Besides conventional label applications, surface protection of articlesof use plays an important role. A protective film which can later beremoved again without problems is applied to scratch-sensitive andfragile materials, such as, for example, glass, for transport. To thisend, a certain adhesion of the film to the material to be protected isnecessary in order that the protective film does not fall offprematurely. At the same time, however, the adhesion must not beexcessively great in order that trace-free removal is facilitated. Ithas been found that embodiments with a copolymer as additive, inparticular a propylene copolymer, such as, for example,propylene-ethylene copolymers having a C2 content of from 2 to 10% byweight, are particularly advantageous for these applications, it beingpossible for this purpose to increase the content of copolymer up to 50%by weight, based on the weight of the top layer.

The inner top layer may additionally comprise conventional additives,such as neutralisers, stabilisers, antistatics, antiblocking agentsand/or lubricants, in effective amounts in each case. The data in % byweight below are in each case based on the weight of the inner toplayer. Particular preference is given to embodiments which additionallycomprise antiblocking agents in the inner top layer. It has been foundthat the antiblocking agent contributes towards reducing the deposits(pick-off) during production of the film.

Suitable antiblocking agents are inorganic additives, such as silicondioxide, calcium carbonate, magnesium silicate, aluminium silicate,calcium phosphate and the like, and/or incompatible organic polymers,such as polyamides, polyesters, polycarbonates and the like, orcrosslinked polymers, such as crosslinked polymethyl methacrylate, orcrosslinked silicone oils. Silicon dioxide and calcium carbonate arepreferred. The mean particle size is between 1 and 6 μm, in particular 2and 5 μm. The effective amount of antiblocking agent is in the rangefrom 0.1 to 5% by weight, preferably from 0.5 to 3% by weight, inparticular from 0.8 to 2% by weight.

Lubricants are higher aliphatic acid amides, higher aliphatic acidesters and metal soaps, as well as polydimethylsiloxanes. The effectiveamount of lubricant is in the range from 0.01 to 3% by weight,preferably from 0.02 to 1% by weight, based on the inner top layer.Particularly suitable is the addition of from 0.01 to 0.3% by weight ofaliphatic acid amides, such as erucamide, or from 0.02 to 0.5% by weightof polydimethylsiloxanes, in particular polydimethylsiloxanes having aviscosity of from 5000 to 1,000,000 mm²/s.

In a preferred embodiment, the surface of the inner top layer iscorona-, plasma- or flame-treated. It has been found that a surfacetreatment of this type, in particular the corona treatment, improves theadhesive strength of the inner top layer to the various polymermaterials.

The thickness of the inner top layer is generally greater than 0.3 μmand is preferably in the range from 0.5 to 5 μm, in particular from 1 to3 μm.

In accordance with the invention, films applied to a container with theabove-described inner top layer in the IML method or by thethermolabelling method have very good adhesive strengths not only to PPand PE containers. The adhesive strengths to PVC, PS and PET containersare also excellent. On use in the thermolabelling method, an adhesivestrength of >0.5 N/15 mm, generally >1.0 N/15 mm, is achieved attemperatures of the container wall of 130° C. and at a sealing pressureof 10 N/cm² and at a pressing time of 0.5 sec.

The above-described inner top layer having the composition according tothe invention can advantageously be applied to transparent or opaquebase layers. For the purposes of the present invention, “opaque film”means a non-transparent film whose light transparency (ASTM-D 1003-77)is at most 70%, preferably at most 50%.

For transparent embodiments, the base layer of the film generallycomprises at least 85% by weight, preferably from 90 to <100% by weight,in particular from 95 to 99% by weight, in each case based on the baselayer, of a polyolefin. Polyolefins are, for example, polyethylenes,polypropylenes, polybutylenes or copolymers of olefins having from twoto eight carbon atoms, amongst which polyethylenes and polypropylenesare preferred.

In general, the propylene polymer comprises at least 90% by weight,preferably from 94 to 100% by weight, in particular from 98 to <100% byweight, of propylene. The corresponding comonomer content of at most 10%by weight or from 0 to 6% by weight or from 0 to 2% by weight generallyconsists, if present, of ethylene. The data in % by weight are in eachcase based on the propylene polymer.

Preference is given to isotactic propylene homopolymers having a meltingpoint of from 140 to 170° C., preferably from 150 to 165° C., and a meltflow index (measurement DIN 53 735 at a load of 21.6 N and 230° C.) offrom 1.0 to 10 g/10 min, preferably from 1.5 to 6.5 g/10 min. Then-heptane-soluble content of the polymer is generally from 0.5 to 10% byweight, preferably from 2 to 5% by weight, based on the startingpolymer. The molecular weight distribution of the propylene polymer canvary. The ratio between the weight average molecular weight M_(w) andthe number average molecular weight M_(n) is generally between 1 and 15,preferably from 2 to 10, very particularly preferably from 2 to 6. Sucha narrow molecular weight distribution of the propylene homopolymer ofthe base layer is achieved, for example, by peroxidic degradationthereof or by preparation of the polypropylene by means of suitablemetallocene catalysts.

In a preferred embodiment, the base layer is opaque through the additionof fillers. In general, the base layer in this embodiment comprises atleast 70% by weight, preferably from 75 to 99% by weight, in particularfrom 80 to 98% by weight, in each case based on the weight of the baselayer, of the above-described polyolefins or propylene polymers, wherethe propylene homopolymers described are likewise preferred.

The opaque base layer comprises fillers in a maximum amount of 30% byweight, preferably from 1 to 25% by weight, in particular from 2 to 20%by weight, based on the weight of the base layer. For the purposes ofthe present invention, fillers are pigments and/or vacuole-initiatingparticles.

For the purposes of the present invention, pigments are incompatibleparticles which essentially do not result in vacuole formation when thefilm is stretched. The colouring action of the pigments is caused by theparticles themselves. “Pigments” generally have a mean particle diameterof from 0.01 to a maximum of 1 μm, preferably from 0.01 to 0.7 μm, inparticular from 0.01 to 0.4 μm. Pigments include both so-called “whitepigments”, which colour the films white, and “coloured pigments”, whichgive the film a coloured or black colour. Conventional pigments arematerials such as, for example, aluminium oxide, aluminium sulphate,barium sulphate, calcium carbonate, magnesium carbonate, silicates, suchas aluminium silicate (kaolin clay) and magnesium silicate (talc),silicon dioxide and titanium dioxide, of which preference is given tothe use of white pigments, such as calcium carbonate, silicon dioxide,titanium dioxide and barium sulphate.

The titanium dioxide particles generally consist of at least 95% byweight of rutile and are preferably employed with a coating of inorganicoxides and/or of organic compounds containing polar and nonpolar groups.TiO2 coatings of this type are known in the prior art.

For the purposes of the present invention, “vacuole-initiating fillers”are solid particles which are incompatible with the polymer matrix andresult in the formation of vacuole-like cavities when the films arestretched, with the size, nature and number of the vacuoles beingdependent on the size and amount of the solid particles and thestretching conditions, such as stretching ratio and stretchingtemperature. The vacuoles reduce the density and give the films acharacteristic pearl-like opaque appearance caused by light scatteringat the “vacuole/polymer matrix” interfaces. Light scattering at thesolid particles themselves generally contributes relatively little tothe opacity of the film. In general, the vacuole-initiating fillers havea minimum size of 1 μm in order to give an effective, i.e. opacifying,amount of vacuoles. In general, the mean particle diameter of theparticles is from 1 to 6 μm, preferably from 1.5 to 5 μm. The chemicalcharacter of the particles plays a secondary role, unlessincompatibility exists.

Conventional vacuole-initiating fillers are inorganic and/or organic,polypropylene-incompatible materials, such as aluminium oxide, aluminiumsulphate, barium sulphate, calcium carbonate, magnesium carbonate,silicates, such as aluminium silicate (kaolin clay) and magnesiumsilicate (talc), and silicon dioxide, amongst which calcium carbonateand silicon dioxide are preferably employed. Suitable organic fillersare the conventional polymers which are incompatible with the polymer ofthe base layer, in particular those such as HDPE, copolymers of cyclicolefins, such as norbornene or tetracyclododecene with ethylene orpropene, polyesters, polystyrenes, polyamides and halogenated organicpolymers, preference being given to polyesters, such as, for example,polybutylene terephthalates. For the purposes of the present invention,“incompatible materials or incompatible polymers” means that thematerial or polymer is in the film in the form of a separate particle orseparate phase.

The opaque base layer comprises pigments in an amount of from 0.5 to 10%by weight, preferably from 1 to 8% by weight, in particular from 1 to 5%by weight. Vacuole-initiating fillers are present in an amount of from0.5 to 30% by weight, preferably from 1 to 15% by weight, in particularfrom 1 to 10% by weight. The data are based on the weight of the baselayer.

The density of the film can vary, depending on the composition of thebase layer, in a range from 0.4 to 1.1 g/cm³. Vacuoles contribute to areduction in the density, whereas pigments, such as, for example, TiO₂,increases the density of the film owing to its relatively high specificweight. The density of the film is preferably from 0.5 to 0.95 g/cm³.

In addition, the base layer can, both in a transparent and in an opaqueembodiment, comprise conventional additives, such as neutralisers,stabilisers, antistatics and/or lubricants, in effective amounts in eachcase. The following data in % by weight are in each case based on theweight of the base layer.

Preferred antistatics are glycerol monostearates, alkali metalalkane-sulphonates, polyether-modified, i.e. ethoxylated and/orpropoxylated polydiorganosiloxanes (polydialkylsiloxanes,polyalkylphenylsiloxanes and the like) and/or essentially straight-chainand saturated aliphatic, tertiary amines containing an aliphatic radicalhaving from 10 to 20 carbon atoms which are substituted byω-hydroxy-(C₁–C₄)alkyl groups, where N,N-bis(2-hydroxyethyl)alkylamineshaving from 10 to 20 carbon atoms, preferably from 12 to 18 carbonatoms, in the alkyl radical are particularly suitable. The effectiveamount of antistatic is in the range from 0.05 to 0.5% by weight.

Lubricants are higher aliphatic acid amides, higher aliphatic acidesters, waxes and metal soaps as well as polydimethylsiloxanes. Theeffective amount of lubricant is in the range from 0.01 to 3% by weight,preferably from 0.02 to 1% by weight. Particularly suitable is theaddition of higher aliphatic acid amides in the range from 0.01 to 0.25%by weight in the base layer. Particularly suitable aliphatic acid amidesare erucamide and stearylamide. The addition of polydimethylsiloxanes ispreferred in the range from 0.02 to 2.0% by weight, in particularpolydimethylsiloxanes having a viscosity of from 5000 to 1,000,000mm²/s.

Stabilisers which can be employed are the conventional stabilisingcompounds for polymers of ethylene, propylene and other α-olefins. Theyare added in an amount of between 0.05 and 2% by weight. Particularlysuitable are phenolic and phosphitic stabilisers, such as tris2,6-dimethylphenyl phosphite. Phenolic stabilisers having a molecularweight of greater than 500 g/mol are preferred, in particulartris-2,6-dimethylphenyl phosphite, pentaerythrityltetrakis-3-(3,5-di-tertiary-butyl-4-hydroxyphenyl)propionate or1,3,5-trimethyl-2,4,6-tris(3,5-di-tertiary-butyl-4-hydroxybenzyl)benzene.Phenolic stabilisers are employed here alone in an amount of from 0.1 to0.6% by weight, in particular from 0.1 to 0.3% by weight, phenolic andphosphitic stabilisers in the ratio from 1:4 to 2:1 and in a totalamount of from 0.1 to 0.4% by weight, in particular from 0.1 to 0.25% byweight.

Neutralisers are preferably dihydrotalcite, calcium stearate and/orcalcium carbonate having a mean particle size of at most 0.7 μm, anabsolute particle size of less than 10 μm and a specific surface area ofat least 40 m²/g. In general, from 0.02 to 0.1% by weight is added.

For two-layered embodiments, which have only one inner top layer, it ispreferred that the outer surface of the base layer is surface-treated bymeans of corona, plasma or flame.

The polyolefin film according to the invention preferably has a second,outer top layer which exhibits good adhesion to conventional printinginks, adhesives, and coatings and/or lacquers. This outer top layer ofthe film is preferably applied to the opposite surface of the base layerand is referred to below as “outer top layer”. In order further toimprove the adhesion of printing inks, adhesives and coatings, it ispreferred to carry out a corona, plasma or flame treatment of thesurface of the outer top layer.

The outer top layer is generally built up from polymers of olefinshaving from 2 to 10 carbon atoms. The outer top layer generallycomprises from 95 to 100% by weight of polyolefin, preferably from 98 to<100% by weight of polyolefin, in each case based on the weight of thetop layer(s).

Examples of suitable olefinic polymers of the top layer(s) are propylenehomopolymers, copolymers or terpolymers II comprising ethylene,propylene and/or butylene units or mixtures of the said polymers. Thesecopolymers or terpolymers II contain no carboxylic acid monomers (oresters thereof). They are polyolefins. Of these, preferred polymers arerandom ethylene-propylene copolymers having an ethylene content of from1 to 10% by weight, preferably from 2.5 to 8% by weight, or randompropylene-1-butylene copolymers having a butylene content of from 2 to25% by weight, preferably from 4 to 20% by weight, or randomethylene-propylene-1-butylene terpolymers having an ethylene content offrom 1 to 10% by weight and a 1-butylene content of from 2 to 20% byweight, or a mixture or blend of ethylene-propylene-1-butyleneterpolymers and propylene-1-butylene copolymers having an ethylenecontent of from 0.1 to 7% by weight and a propylene content of from 50to 90% by weight and a 1-butylene content of from 10 to 40% by weight.The data in % by weight are in each case based on the weight of thepolymer.

The above-described copolymers and/or terpolymers II employed in theouter top layer generally have a melt flow index of from 1.5 to 30 g/10min, preferably from 3 to 15 g/10 min. The melting point is in the rangefrom 120 to 145° C. The above-described blend of copolymers andterpolymers II has a melt flow index of from 5 to 9 g/10 min and amelting point of from 120 to 150° C. All the melt flow indices indicatedabove are measured at 230° C. and a force of 21.6 N (DIN 53 735). Ifdesired, all the top-layer polymers described above can have beenperoxidically or also thermooxidatively degraded, with the degradationfactor generally being in a range from 1 to 15, preferably from 1 to 8.

If desired, the above-described additives, such as antistatics,neutralisers, lubricants and/or stabilisers, and, if desired,additionally antiblocking agents can be added to the outer top layer(s).The data in % by weight are then based correspondingly on the weight ofthe top layer.

Suitable antiblocking agents have already been described in connectionwith the inner top layer. These antiblocking agents are also suitablefor the outer top layer. The preferred amount of antiblocking agent forthe outer top layer is in the range from 0.1 to 2% by weight, preferablyfrom 0.1 to 0.8% by weight.

The thickness of the outer top layer is generally greater than 0.1 μmand is preferably in the range from 0.1 to 5 μm, in particular from 0.3to 2 μm.

In a particularly preferred embodiment, the surface of the outer toplayer is corona-, plasma- or flame-treated. This treatment serves toprepare the film surface for subsequent decoration and printing, i.e. toensure wettability with and adhesion of printing inks and otherdecoration agents.

The film according to the invention comprises at least the base layerdescribed above and the inner top layer, comprising copolymer orterpolymer I and additive. If desired, a second, outer top layer isapplied to the opposite surface. If desired, an interlayer orinterlayers may also be present on one or both sides between the baselayer and the top layer(s).

The interlayer(s) can be built up from the olefinic polymers, preferablypropylene polymers, described for the base layer or for the top layers.The interlayer(s) can comprise the conventional additives described forthe individual layers, such as antistatics, neutralisers, lubricantsand/or stabilisers. In a further embodiment, an additive as describedabove for the inner top layer can likewise be added to the interlayerarranged between the base layer and the inner top layer. Preferredadditives are likewise the polyolefins, polystyrene, polyesters,polyamides, hydrocarbon and wax described. The content of additive inthe interlayer is at most 30% by weight and is preferably in the rangefrom 0.5 to 20% by weight, in each case based on the weight of theinterlayer. The thickness of this interlayer is greater than 0.5 μm andis preferably in the range from 0.6 to 6 μm, in particular from 1 to 4μm.

Of the possible suitable additives, higher aliphatic acid amides higheraliphatic acid esters, such as, for example, erucamide and/orpolysiloxane, such as polydimethylsiloxanes, are particularly suitable,where these additives are employed in conventional or even slightlyincreased amounts. For example, up to 5% by weight of EA or PDMS can beincorporated into the interlayer.

If desired, the interlayer may additionally comprise the antiblockingagents described for the top layers in order additionally to contributetowards the surface roughness.

The interlayer, which, in a preferred embodiment, can be applied betweenthe outer top layer and the base layer (outer interlayer below),contributes to high gloss on the outside of the opaque label, inparticular unfilled (i.e. without vacuole-initiating fillers and withoutTiCl₂) outer interlayers of propylene homopolymer. For embodiments inwhich a white or opaque appearance (high hiding power) of the label isdesired, the outer interlayer comprises vacuole-initiating fillersand/or pigments, in particular TiO₂. The thickness of this outerinterlayer is greater than 0.3 μm and is preferably in the range from1.0 to 15 μm, in particular from 1.5 to 10 μm.

The total thickness of the label film according to the invention canvary within broad limits and depends on the intended use. It ispreferably from 15 to 150 μm, in particular from 20 to 100 μm,preferably from 25 to 90 μm. The base layer makes up from about 40 to99% of the total film thickness.

The invention furthermore relates to a process for the production of thepolyolefin film according to the invention by the coextrusion process,which is known per se. This process is carried out by coextruding themelts corresponding to the individual layers of the film simultaneouslyand jointly through a flat-film die, taking off the resultant film overone or more roll(s) for solidification, subsequently stretching(orienting) the multilayered film, heat-setting the stretched film and,if desired, plasma- corona- or flame-treating the surface layer intendedfor the treatment.

Biaxial stretching (orientation) is carried out sequentially orsimultaneously. The sequential stretching is generally carried outconsecutively, with consecutive biaxial stretching, in which stretchingis firstly carried out longitudinally (in the machine direction) andthen transversely (perpendicular to the machine direction), beingpreferred. The film production is described further using the example offlat film extrusion with subsequent sequential stretching.

Firstly, as is usual in the extrusion process, the polymer or polymermixture of the individual layers is compressed and liquefied in anextruder, it being possible for any additives added already to bepresent in the polymer or polymer mixture. The melts are then forcedsimultaneously through a flat-film die (slot die), and the extrudedmultilayered film is taken off over one or more take-off rolls at atemperature of from 10 to 100° C., preferably from 10 to 50° C., duringwhich it cools and solidifies.

The film obtained in this way is then stretched longitudinally andtransversely to the extrusion direction, which results in orientation ofthe molecule chains. The longitudinal stretching is preferably carriedout at a temperature of from 70 to 130° C., preferably from 80 to 110°C., advantageously with the aid of two rolls running at different speedscorresponding to the target stretching ratio, and the transversestretching is preferably carried out at a temperature of from 120 to180° C. with the aid of an appropriate tenter frame. The longitudinalstretching ratios are in the range from 3 to 8, preferably from 4 to 6.The transverse stretching ratios are in the range from 5 to 10,preferably from 7 to 9.

In principle, it is necessary for the longitudinal stretching of a filmby means of rolls to warm the film to a minimum temperature through theroll contact in order that uniform stretching is possible. In connectionwith the present invention, it has been found that the top layercomprising copolymers or terpolymers I have an increased tendency tostick to the rolls of the longitudinal stretching unit. It has beenfound that a film whose top layer consists only of copolymers orterpolymers I cannot be stretched in the longitudinal direction by meansof rolls using the conventional stenter process. If the temperatures aretoo high, deposits on the longitudinal stretching rolls result inoptical defects. At lower temperatures, stretch arcs and tears occur. Ithas not been possible to find a suitable temperature range in which thefilm can be produced on a production scale.

Surprisingly, the additives described in the top layer significantlyreduce the tendency of the top-layer raw material to stick and depositson the longitudinal stretching rolls. It has thus been possible to finda temperature range which allows the production of the film on aproduction scale. It has been found that the addition of the waxes,polyethylenes or other additives makes possible longitudinal stretchingat a temperature in the region of the melting point of the particulartop-layer raw material. Preference is given to a temperature in theregion of 10° C., preferably 5° C., above or below the melting point ofthe copolymer or terpolymer I.

The stretching of the film is followed by heat-setting (heat treatment)thereof, in which the film is held at a temperature from 100 to 160° C.for from about 0.1 to 10 seconds. The film is subsequently wound up in aconventional manner by means of a wind-up device.

After the biaxial stretching, one or both surface(s) of the film is(are) preferably plasma-, corona- or flame-treated by one of the knownmethods. The treatment intensity is generally in the range from 35 to 50mN/m, preferably from 37 to 45 mN/m.

In the case of corona treatment, an advantageous procedure is to passthe film between two conductor elements serving as electrodes, with sucha high voltage, usually an alternating voltage (from about 5 to 20 kVand from 5 to 30 kHz), being applied between the electrodes that sprayor corona discharges are able to occur. Due to the spray or coronadischarge, the air above the film surface is ionised and reacts with themolecules of the film surface, causing the formation of polar inclusionsin the essentially non-polar polymer matrix.

The surface treatment, such as, for example, corona treatment, can becarried out immediately during production of the label film or at alater point in time, for example immediately before the labellingoperation.

In accordance with the invention, the label film is employed in variousmethods for the labelling of plastic containers, in particular for thein-mould and thermolabelling method, it being unnecessary here foradhesives or adhesion promoters, coatings or similar auxiliaries to beapplied in a separate working step after the film production.

Furthermore, it has been found that the labels also adhere very well toother materials, such as, for example, glass, aluminium, wood ortinplate, with labelling by means of thermolabelling being suitable inthe case of these materials.

The thermoplastic polymer containers to be labelled can be or have beenproduced by a very wide variety of processes and from a very widevariety of materials. The containers can have either solid walls orfoamed walls. The latter can be foamed in the mould from granularprecursors containing corresponding blowing agents or shaped from foamedsheets by thermoforming. Depending on the requirements of the containerand the process for the production thereof, various materials, such aspolypropylene (PP), high- or low-density polyethylene (HD-PE or LD-PE orLLD-PE), polystyrene (PS), polyvinyl chloride (PVC), polyethyleneterephthalate (PET), copolymers thereof and other polymers, inindividual cases also mixtures of such polymers, are thus employed forthe production of the containers. Processes for the production of thecontainers are, for example, injection moulding, thin-wall injectionmoulding, blow moulding, thermoforming or injection stretch blowmoulding.

The labelling of the thermoplastic polymer containers with the labelfilm according to the invention can be carried out by the IML method andcombined with all the standard processes mentioned for the production ofcontainers. A feature that is common to all variants or combinations isthat the label is cut to size before the shaping or production of thecontainer (cut-in-place or cut & stack) and laid in the mould in such away that the printed outside of the label is in contact with the mouldand later forms the visible side of the container. The inside of thelabel faces the container. During the shaping or production of thecontainer, the inner surface of the label bonds to the container underthe action of pressure and temperature.

The temperatures and pressures to be used during the shaping orproduction of the thermoplastic polymer container depend on theproperties of the moulding compositions employed and on the requirementsof the selected process for the production or shaping of the container.These conditions are outlined in various handbooks of plasticsprocessing (inter alia “Kunststoff-Taschenbuch”, edited by Hj.Saechtling, Hanser-Verlag Munich-Vienna) and in the recommendations ofthe manufacturers of the corresponding moulding compositions.

The label film can also be employed in accordance with the invention forthe labelling of containers by the thermolabelling method. For thepurposes of the present invention, thermolabelling is a labelling methodin which the label is applied under the action of heat (withoutadditional auxiliaries) to a container which has been produced inadvance, i.e. in a separate working step. A surprisingly large number ofcontainer materials can be labelled, for example glass, metal, such as,for example, tinplate or aluminium, or also thermoplastic polymers,which have been described above for the in-mould label method.

It is not necessary in accordance with the invention for the labeladditionally to be provided with coupling agents and auxiliaries,adhesives or coatings on the inside. All that is needed is the action ofheat and, if necessary, additionally pressure in order to apply thelabel with its inner top layer to the surface of the container wall.Either the label and/or the pre-shaped container can be heated to asuitable temperature range in a separate process step, after productionof the container, but before application of the label, where thecontainer should remain as dimensionally stable as possible at thesetemperatures. The suitable temperature range depends on the material ofthe container and is, for example, from 90 to 140° C. for PP, from 70 to120° C. for PE-HD, from 60 to 115° C. for PE-LD and PE-LLD, from 130 to170° C. for PET, from 110 to 145° C. for PC, from 70 to 130° C. forrigid PVC, from 50 to 120° C. for flexible PVC, depending on theformulation, and from 70 to 95° C. for PS. During labelling with thelabel film according to the invention, a temperature range of from 95 to130° C. is preferably maintained for PP, from 75 to 115° C. for PE-HD,from 65 to 105° C. for PE-LD and PE-LLD, from 135 to 165° C. for PET,from 120 to 140° C. for PC, from 80 to 125° C. for rigid PVC, from 60 to120° C. for flexible PVC, depending on the formulation, and from 75 to90° C. for PS.

The additional use of a suitable contact pressure together with theaction of heat may be helpful. The pressure here can act over the entirearea of the label by, for example, corresponding “heat-sealing tools” orrams pressing the label flat onto the container. The prerequisite forthis is a flat container shape in the region of the label to be applied.Rolls or brushes may, if desired, be passed over the label and thuspress the label on over its entire area. This is particularlyadvantageous in the case of round container shapes. The contact pressurecan vary within broad limits and is dependent on the method and thecontainer shape.

In particular in the case of containers having thin and flat walls,preferred method variants are those in which the container wall isstabilised by a corresponding counterpressure. In the case of pots anddishes, female moulds or counter pressure rolls lying against the innerwall and also an excess pressure of air, particularly in the case ofbottles, are suitable for this purpose.

If desired, the label can also only be bonded to the container wall on apart area (patch labelling). In this variant, an adhesive is applied tothe label over the entire area in accordance with the prior art, and thelabel is subsequently applied to the container wall. In the case of thelabel film according to the invention, the application of adhesive isunnecessary. One or more labels can be applied to a container in thisway.

A further variant of subsequent container labelling is wrap-aroundlabelling, in which the label in the form of a strip is wrapped aroundthe container and only bonded to the container wall or to the labelitself at the ends of the strip by application of a hot-melt adhesive,which provides adhesion of the label to the container or of the label toitself. In the case of the film according to the invention, theapplication of adhesive is unnecessary. All that is needed is warming inthe region of the strip, which adheres to the container or to the film.

Depending on the method variant selected, it may be advantageous also oronly to heat the label film before application. In these cases, thepreferred temperature range of the inner film surface is from 70 to 130°C., particularly preferably from 80 to 125° C. Surprisingly, only verylow temperatures are necessary in order to produce good adhesion of thelabel by means of thermolabelling.

Depending on the printing method used, the process for the production ofthe containers and the machinery at the site of label application, thelabels can be delivered by the “cut-in-place” or by the “cut & stack”method.

In a further application, the label film may also be employed as aconstituent of a laminate, which can itself be used in the mannerdescribed as in-mould or thermolabelling label. The label filmsaccording to the invention then forms the inside of the laminate, sothat, in accordance with the invention, the inner surface of the labelfilm faces the container in the same way and ensures good adhesion tothe container. More or less thin, transparent films, in particulartransparent BOPP films, are typically used on the outside of the label.The print motif here is located between the inner and outer films. Thetwo films are bonded to one another by means of a suitable adhesive.

Measurement Methods

The raw materials and films were characterized using the followingmeasurement methods:

Melt Flow Index

The melt flow index was measured in accordance with DIN 53 735 at a loadof 21.6 N and at 230° C.

Melting Point

DSC measurement, maximum of the melting curve, heating rate 20° C./min.

Haze

The haze of the film was measured in accordance with ASTM-D 1003-52.

Gloss

The gloss was determined in accordance with DIN 67 530. The reflectorvalue was measured as an optical parameter for the surface of a film. Inaccordance with the standards ASTM-D 523-78 and ISO 2813, the angle ofincidence was set at 60° or 85°. A light beam hits the planar testsurface at the set angle of incidence and is reflected or scatteredthereby. The light beams incident on the photoelectronic receiver areindicated as a proportional electrical quantity. The measurement valueis dimensionless and must be specified together with the angle ofincidence.

Surface Tension

The surface tension was determined by the so-called ink method (DIN 53364).

Printability

The corona-treated films were printed 14 days after production(short-term assessment) and 6 months after production (long-termassessment). The ink adhesion was assessed by an adhesive-tape test. Ifa small amount of ink was removable by means of an adhesive tape, theink adhesion was assessed as moderate, and if a significant amount ofink was removed, it was assessed as poor.

Roughness Measurement

As a measure of the roughness of the insides of the films, the roughnessvalues Rz of the films were measured in accordance with DIN 4768 Part 1and DIN 4777, as well as DIN 4772 and 4774 by means of an S8Pperthometer from Feinprüf Perthen GmbH, Göttingen, by the profilemethod. The measurement head, a single-skid probe system in accordancewith DIN 4772, was fitted with a probe tip having a radius of 5 μm andan cone angle of 90° with a probe force of from 0.8 to 1.12 mN and askid having a radius of 25 mm in the sliding direction. The verticalmeasurement range was set to 62.5 μm, the probe zone to 5.6 mm and thecut-off of the RC filter in accordance with DIN 4768/1 to 0.25 mm.

Production of the Films

EXAMPLE 1

A transparent three-layered film consisting of the base layer B, aninner top layer A and an outer top layer C and having a total thicknessof 60 μm was produced by coextrusion and subsequent stepwise orientationin the longitudinal and transverse directions. The top layer A had athickness of 2.0 μm and the top layer C had a thickness of 0.7 μm. Thelayers had the following compositions:

Base layer B: 99.64% by weight of propylene homopolymer having a meltingpoint of 165° C. and a melt flow index of 3.4 g/10 min and a chainisotacticity index of 94%  0.10% by weight of erucamide (lubricant) 0.10% by weight of Armostat 300 (antistatic)  0.03% by weight ofneutraliser (CaCO3)  0.13% by weight of stabiliser (Irganox) Top layerA:  94.5% by weight of terpolymer of ethylene, ethyl acrylate and maleicanhydride having an ethylene content of 91% by weight an ethyl acrylatecontent of 5% by weight and a maleic anhydride content of 4% by weight,based on the terpolymer. The melt flow index was 5.0 g/10 min [at 190°C., 21.6 N]  0.5% by weight of SiO2 as antiblocking agent having a meanparticle size of 4 μm  5.0% by weight of polyethylene wax having amolecular weight Mn (number average) of 2000 Top layer C: 99.54% byweight of random copolymer of ethylene and propylene having a melt flowindex of 6.0 g/10 min and an ethylene content of 6% by weight, based onthe copolymer  0.22% by weight of SiO2 as antiblocking agent having amean particle size of 4 μm  0.20% by weight of stabiliser (Irganox1010/Irgafos 168)  0.04% by weight of neutraliser (Ca stearate)

The production conditions in the individual process steps were asfollows:

Extrusion: Temperatures Base layer B: 260° C. Top layer A: 230° C. Toplayer C: 240° C. Temperature of the take-off  20° C. roll: LongitudinalTemperature: 100° C. stretching: Longitudinal stretching 1:4.5 ratio:Transverse Temperature: 165° C. stretching: Transverse stretching ratio:1:9   Setting: Temperature: 140° C. Convergence: 10% Pressure Top layerA Corona pretreatment 10,000 V/10,000 Hz Top layer C Corona 10,000V/10,000 Hz

The transverse stretching ratio of 1:9 is an effective value. Thiseffective value is calculated from the final film width B reduced bytwice the hem width b divided by the width of the longitudinallystretched film C, likewise reduced by twice the hem width b.

EXAMPLE 2

A three-layered film as described in Example 1 was produced. In contrastto Example 1, 5.1% by weight of calcium carbonate (chalk) having a meanparticle diameter of 2 μm were additionally incorporated into the baselayer as vacuole-initiating particles (chalk). The polypropylene contentwas reduced correspondingly. The production conditions in the individualprocess steps were as in Example 1. The film was opaque. In addition,the composition of the top layer A was modified as follows:

Top layer A: 92.5% by weight of terpolymer of ethylene, ethyl acrylateand maleic anhydride having an ethylene content of 91% by weight ethylacrylate content of 5% by weight and a maleic anhydride content of 4% byweight, based on the terpolymer. The melt flow index was 5.0 g/10 min[at 190° C., 21.6 N]  0.5% by weight of SiO2 as antiblocking agenthaving a mean particle size of 4 μm  2.0% by weight of polyethylene waxhaving a molecular weight Mn (number average) of 2000  5.0% by weight ofHDPE having an MFI of 15 g/10 min (190° C./ 2.16 kg) and a melting pointof 133° C. (DSC@10° C./min)

In addition to the labelling applications described below, the film wasused as lid film and applied to yoghurt pots made from polystyrene andto a casting part made from polypropylene. The film exhibited goodadhesion to both the containers and could subsequently be removed easilyand without leaving a residue. The good adhesion was achieved attemperatures of only about 80° C. The heat-sealing rim of the yoghurtpot thus remained reliably dimensionally stable.

EXAMPLE 3

A three-layered film as described in Example 2 was produced. In contrastto Example 2, 2.8% by weight of titanium dioxide (rutile) wereadditionally incorporated into the base layer as pigment. Thepolypropylene content was reduced correspondingly. The productionconditions in the individual process steps were as in Example 2. Thefilm was white opaque. In addition, the composition of the top layer Awas modified as follows:

Top layer A: 89.5% by weight of terpolymer of ethylene, ethyl acrylateand maleic anhydride having an ethylene content of 91% by weight ethylacrylate content of 5% by weight and a maleic anhydride content of 4% byweight, based on the terpolymer. The melt flow index was 5.0 g/10 min[at 190° C., 21.6 N]  0.5% by weight of SiO2 as antiblocking agenthaving a mean particle size of 4 μm 10.0% by weight of HDPE having anMFI of 15 g/10 min (190° C./ 2.16 kg) and a melting point of 133° C.(DSC@10° C./min)

EXAMPLE 4

A film as described in Example 3, but with an additional interlayer, wasproduced. The interlayer D was applied between the base layer B and thetop layer C and was built up from pure propylene homopolymer having amelting point of 165° C. and a melt flow index of 3.4 g/10 min and achain isotacticity index of 94%. The production conditions in theindividual process steps were as in Example 3. In addition, thecomposition of the top layer A was modified as follows:

Top layer A: 89.5% by weight of terpolymer of ethylene, ethyl acrylateand maleic anhydride having an ethylene content of 91% by weight ethylacrylate content of 5% by weight and a maleic anhydride content of 4% byweight, based on the terpolymer. The melt flow index was 5.0 g/10 min[at 190° C., 21.6 N]  0.5% by weight of SiO2 as antiblocking agenthaving a mean particle size of 4 μm 10.0% by weight of random copolymerof ethylene and propylene having a melt flow index of 6.0 g/10 min andan ethylene content of 6% by weight, based on the copolymer

EXAMPLE 5

A film as described in Example 4, but with a second interlayer E on theopposite side, was produced. In addition, the composition of the toplayer A was modified as follows:

Top layer A: 87.5% by weight of terpolymer of ethylene, ethyl acrylateand maleic anhydride having an ethylene content of 91% by weight ethylacrylate content of 5% by weight and a maleic anhydride content of 4% byweight, based on the terpolymer. The melt flow index was 5.0 g/10 min[at 190° C., 21.6 N]  0.5% by weight of SiO2 as antiblocking agenthaving a mean particle size of 4 μm  2.0% by weight of polyethylene waxhaving a molecular weight Mn (number average) of 2000 10.0% by weight ofrandom copolymer of ethylene and propylene having a melt flow index of6.0 g/10 min and an ethylene content of 6% by weight, based on thecopolymer

The interlayers D and E had the following compositions:

First interlayer D: 90.58% by weight of propylene homopolymer having amelting point of 165° C. and a melt flow index of 3.4 g/10 min and achain isotacticity index of 94%  9.0% by weight of titanium dioxide(rutile) as pigment  0.12% by weight of erucamide  0.14% by weight ofArmostat 300  0.03% by weight of neutraliser (CaCO3)  0.13% by weight ofstabiliser (Irganox) Second interlayer E: 97.58% by weight of randomcopolymer of ethylene and propylene having a melt flow index of 6.0 g/10min and an ethylene content of 6% by weight, based on the copolymer 2.0% by weight of polydimethylsiloxane (PDMS) having a viscosity of30,000 mm²/s  0.18% by weight of erucamide  0.20% by weight ofstabiliser (Irganox 1010/Irgafos 168)  0.04% by weight of neutraliser(Ca stearate)

The production conditions in the individual process steps were as inExample 2.

COMPARATIVE EXAMPLE 1

A transparent three-layered film as described in Example 1 was produced.In contrast to Example 1, the terpolymer of ethylene, ethyl acrylate andmaleic anhydride in the inner top layer A was replaced by a randomcopolymer of ethylene and propylene having a melt flow index of 6.0 g/10min and an ethylene content of 6% by weight, based on the copolymer. Theproduction conditions in the individual process steps were as in Example1.

COMPARATIVE EXAMPLE 2

An opaque three-layered film as described in Example 2 was produced. Incontrast to Example 2, the terpolymer of ethylene, ethyl acrylate andmaleic anhydride in the inner top layer A was replaced by a randomcopolymer of ethylene and propylene having a melt flow index of 6.0 g/10min and an ethylene content of 6% by weight, based on the copolymer. Theproduction conditions in the individual process steps were as in Example2.

COMPARATIVE EXAMPLE 3

A three-layered white opaque film as described in Example 3 wasproduced. In contrast to Example 3, the HDPE content of the inner toplayer A was increased to 50% by weight. The production conditions in theindividual process steps were as in Example 3.

COMPARATIVE EXAMPLE 4

A four-layered white opaque film as described in Example 4 was produced.In contrast to Example 3, the copolymer content of the inner top layer Awas increased to 50% by weight. The production conditions in theindividual process steps were as in Example 4.

COMPARATIVE EXAMPLE 5

A five-layered white opaque film as described in Example 5 was produced.In contrast to Example 3, the copolymer content of the inner top layer Awas increased to 25% by weight. The production conditions in theindividual process steps were as in Example 5.

COMPARATIVE EXAMPLE 6

It was attempted to produce a three-layered, white opaque film asdescribed in Example 1. In contrast to Example 1, no polyethylene wax orSylobloc were added. The production conditions in the individual processsteps were as in Example 1. Owing to massive deposits on thelongitudinal stretching rolls, it was not possible to produce a film.

The films of the examples and comparative examples were employed inin-mould and thermolabelling methods and compared with respect to theiradhesion properties. For the in-mould test series, various containermaterials were injected into a container mould at the respective usualprocessing temperatures for the polymer. Before the actual injectionoperation, a film in accordance with the examples and comparativeexamples was laid in the container mould in such a way that the insideof the film was facing the container to be shaped. After production ofthe labelled container, the adhesive strength of the respective labelwas tested. The results are shown in Table 1.

For the thermolabelling test series, containers made from variouspolymers were employed. In individual cases, such as, for example, inthe case of glass containers, the container was pre-warmed slightly(about 50–60° C.). A corresponding film piece was ironed onto therespective container under the action of a manual contact pressure at atemperature of from 120 to 130° C. by means of a hand heat-sealingpiston. After the container labelled way had cooled to room temperature,the adhesive strengths were gated. The results are shown in Table 2.

TABLE 1 IML PET/ Example PP PE PETE PS PVC PC 1 +++ +++ +++ +++ +++ +++2 +++ +++ +++ +++ +++ +++ 3 +++ +++ +++ +++ +++ +++ 4 +++ +++ ++ ++ ++++ 5 +++ +++ +++ ++ ++ ++ C1 +++ + − − − − C2 +++ + − − − − C3 +++ +++ −− − − C4 +++ ++ − − − − C5 +++ ++ + − − −

TABLE 2 Thermolabelling PET/ Tinplate/ Example PP PE PETE PS PVC PCGlass aluminium 1 +++ +++ +++ +++ +++ +++ +++ +++ 2 +++ +++ +++ +++ ++++++ +++ +++ 3 +++ +++ +++ +++ +++ +++ +++ +++ 4 +++ ++ ++ ++ ++ ++ ++++++ 5 +++ ++ ++ ++ ++ ++ +++ +++ C1 +++ + − − − − − − C2 +++ + − − − − −− C3 +++ ++ − − − − + + C4 +++ ++ − − − − − + C5 +++ ++ + − − − ++ ++Assessment criteria: +++ very good adhesion > 1.5 N/15 mm ++ goodadhesion >> 0.5 N/15 mm + very weak adhesion ≧ 0.5 N/15 mm − no adhesionat all

1. Method of making a label film, which method comprises converting abiaxially oriented multilayered coextruded polyolefin film comprising(i) a base layer comprising polypropylene and (ii) at least oneadhesion-promoting layer, wherein this adhesion-promoting layercomprises at least about 70% by weight of a copolymer (I) or terpolymer(I) built up from at least an olefin and an unsaturated carboxylic acid,and (b) from 1 to 30% by weight of a deposit preventing additiveconsisting of one or more of wax, polystyrene, polyester, polyamide andhigh density polyethylene, wherein the % by weight are in each casebased on the weight of the adhesion-promoting layer, into a label film.2. Method of making a label film, which method comprises converting abiaxially oriented multilayered coextruted polyolefin film comprising abase layer and at least one adhesion-promoting layer into a label film,said adhesion-promoting layer comprising (a) at least about 70% byweight of a copolymer (I) or terpolymer (I) built up from at least anolefin and an unsaturated carboxylic acid or ester thereof or ananhydride thereof and (b) not more than 30% by weight of a depositpreventing additive, wherein the % by weight are in each case based onthe weight of the adhesion-promoting layer, wherein said label filmexhibits an adhesive strength of greater than 1.0 N/15 mm to one or moreof a PP container, a PE container, a PVC container, a PS container or aPET container and said copolymer or terpolymer is present within theadhesion-promoting layer alone.
 3. Process for the production of apolyolefin film by the coextrusion process, in which the meltscorresponding to the individual layers of the film are coextrudedsimultaneously and jointly through a flat-film die, the resultant filmis taken off over one or more roll(s) for solidification, themultilayered film is subsequently stretched, the stretched film isheat-set, wherein the film has a adhesion-promoting layer whichcomprises (a) at least about 70% by weight of a terpolymer presentwithin the adhesion-promoting layer alone, said terpolymer built up from(i) olefin (ii) an unsaturated carboxylic acid or ester thereof or ananhydride thereof selected from acrylic acid or methacrylic acid and(iii) an unsaturated monocarboxylic acid ester or an unsaturateddicarboxylle acid or anhydride thereof selected from glycidylmethacrylate, maleic acid or maleic anhydride, and (b) not more than 30%by weight of a deposit preventing additive, wherein the % by weight arein each case based on the weight of the adhesion-promoting layer, andthe longitudinal stretching of the film is carried out by means ofheated rolls, and the temperature during the longitudinal stretchingvaries in a range from about 10° C. above or below the melting point ofthe copolymer or terpolymer.
 4. Method of making a labeled wood,ceramic, glass or metal, which method comprises labeling a biaxiallyoriented multilayered coextruded polyolefin film comprising a base layerand at least one adhesion-promoting layer, wherein thisadhesion-promoting layer comprises at least about 50% by weight of acopolymer (I) or terpolymer (I) present within said adhesion-promotinglayer alone, said copolymer (I) or terpolymer (I) built up from at leastan olefin and an unsaturated carboxylic acid or ester thereof or ananhydride thereof, and not more than 50% by weight of a depositpreventing additive, wherein the % by weight are in each case based onthe weight of the adhesion-promoting layer, onto wood, ceramic, glass ormetal by the thermolabelling method.
 5. Method according to claim 4,wherein the metal is aluminum or tin.
 6. Method of making a multilayeredcomposite, which method comprises laminating a biaxially orientedmultilayered coextruded polyolefin film comprising a base layer and atleast one adhesion-promoting layer, wherein this adhesion-promotinglayer comprises at least about 70% by weight of a copolymer (I) orterpolymer (I) present within said adhesion-promoting layer alone, saidcopolymer (I) or terpolymer (I) built up from at lout an olefin and anunsaturated carboxylic acid or ester thereof or an anhydride thereof,and not more than 30% by weight of a deposit preventing additive,wherein the % by weight are in each case based on the weight of theadhesion-promoting layer, against a further thermoplastic polymer filmor against a paper, wood or metal substrate.
 7. Method of making a lid,which method comprises converting a biaxially oriented multilayeredcoextruded polyolefin film comprising a base layer and at least oneadhesion-promoting layer into a lid, wherein this adhesion-promotinglayer comprises (a) at least about 70% by weight of a terpolymer (I)present within said adhesion-promoting layer alone, said terpolymer (I)built up from (i) olefin (ii) an unsaturated carboxylic acid or esterthereof or an anhydride thereof selected from acrylic acid ormethacrylic acid and (iii) an unsaturated monocarboxylic acid ester oran unsaturated dicarboxylic acid or anhydride thereof selected fromglycidyl methacrylate, maleic acid or maleic anhydride, and (b) not morethen 30% by weight of a deposit preventing additive, wherein the % byweight are in each case based on the weight of the adhesion-promotinglayer.
 8. Method according to claim 7, wherein the lid is made from PS,PP, PE, PET, PVC, PC, metal or tinplate.
 9. Method of making a labelfilm, which method comprises converting a biaxially orientedmultilayered coextruded polyolefin film comprising (i) a base layer and(ii) at least one adhesion-promoting layer, wherein thisadhesion-promoting layer comprises (a) at least about 70% by weight of aterpolymer (I), said terpolymer present within said adhesion-promotinglever alone, said terpolymer built up from (i) olefin; (ii) anunsaturated carboxylic acid or ester thereof or an anhydride thereofselected from acrylic acid or methacrylic acid and (iii) an unsaturatedmonocarboxylic acid ester or an unsaturated dicarboxylic acid oranhydride thereof selected from glycidyl methacrylate, maleic acid ormaleic anhydride, and (b) not more than 30% by weight of a depositpreventing additive, wherein the % by weight are in each case based onthe weight of the adhesion-promoting layer, into a label film. 10.Method according to claim 9, wherein the additive is a wax.
 11. Methodaccording to claim 10, wherein the wax is a polyethylene wax or amacrocrystalline paraffin (paraffin wax) or a microcrystalline wax(microwax).
 12. Method according to claim 10 or 11, wherein the wax hasa mean molecular weight Mn (number average) Mn of from about 200 toabout
 5000. 13. Method according to claim 12, wherein Mn is from about200 to about
 1000. 14. Method according to claim 10 or 11, wherein thewax has a melting point of from about 70 to about 120° C.
 15. Methodaccording to claim 9 or 10, wherein the wax is a polyethylene wax havinga weight average to number average ratio Mw/Mn of from about 1 to about2, and wherein the wax is present in an amount of from about 0.5 toabout 30% by weight, based on the weight of the layer.
 16. Methodaccording to claim 9, wherein the polyolefin film has on the side of thebase layer opposite the adhesion-promoting layer, a second outer toplayer built up from one or more of copolymers II and terpolymers II. 17.Method according to claim 16, wherein the surface of the outer top layeris corona- , plasma- or flame-treated.
 18. Method according to claim 16,wherein the outer top layer comprises antiblocking agents.
 19. Methodaccording to claim 18, wherein the antiblocking agent is SiO₂. 20.Method according to claim 9 or 16, wherein one or more interlayer(s) ofolefinic polymers is (are) on one or both sides between the base layerand the top layer(s).
 21. Method according to claim 20, wherein theinterlayer arranged below the adhesion-promoting layer comprisesadditives.
 22. Method according to claim 21, wherein the additive isselected from one or more of waxes, hydrocarbon resin, polystyrene,polyester, polyamide and linear or branched polyethylene of low (LLDPE,LDPE), medium or high (HDPE) density.
 23. Method according to claim 21,wherein the additive comprises one or more compounds selected from thegroup consisting of lubricants, antistatics and antiblocking agents. 24.Method according to claim 9, wherein the thickness of the film is fromabout 15 to about 150 μm.
 25. Method according to claim 24, wherein thethickness of the film is from about 25 to about 90 μm.
 26. Methodaccording to claim 9 or 24, wherein the base layer makes up from about40 to about 60% of the total thickness.
 27. Method recording to claim 9,wherein the additive is a polyolefin, a hydrocarbon resin, polystyrene,polyester or polyamide.
 28. Method according to claim 27, wherein theadditive is a propylene copolymer or terpolymer, a linear and branchedpolyethylene of low (LLDPE, LDPE), medium or high (HDPE) density. 29.Method according to claim 9, wherein the adhesion-promoting layercomprises from about 70 to about 99.5% by weight of the terpolymer (I).30. Method according to claim 9, wherein the terpolymer I comprises from(a) about 65 to about 96% by weight of olefin, and (b) about 3 to about34% by weight of unsaturated carboxylic acids or esters thereof selectedfrom acrylic acid or methacrylic acid, and (c) about 1 to about 10% byweight of an unsaturated mono- or dicarboxylic acid or an ester thereofor an anhydride thereof which is different from (b) selected fromglycidyl methacrylate, maleic acid or maleic anhydride.
 31. Methodaccording to claim 30, wherein the olefin is ethylene.
 32. Methodaccording to claim 30, wherein the unsaturated carboxylic acids oresters thereof is acrylic acid or esters thereof.
 33. Method accordingto claim 32, wherein the unsaturated carboxylic acid is a methyl, ethyl,n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl or tert-butyl acrylate.34. Method according to claim 30, wherein the unsaturated mono- ordicarboxylic acid or ester thereof or anhydride thereof which isdifferent form (b) is maleic anhydride or glycidyl methacrylate. 35.Method according to claim 9, wherein the adhesion-promoting layercomprises antiblocking agents.
 36. Method according to claim 35, whereinthe adhesion-promoting layer comprises from about 1 to about 5% byweight antiblocking agents.
 37. Method according to claim 9, wherein theadhesion-promoting layer comprises a lubricant.
 38. Method according toclaim 37, wherein the lubricant is selected from one or more oferucamide and polydimethylsiloxane.
 39. Method according to claim 9,wherein the adhesion-promoting layer comprises a mixture of two or moredeposit preventing additives.
 40. Method according to claim 39, whereinthe mixture comprises a wax in an amount of from about 1 to about 10% byweight and HDPE in an amount of from about 1 to about 20% by weight. 41.Method according to claim 9, wherein the adhesion-promoting layer iscorona-, plasma- or flame-treated.
 42. Method according to claim 9,wherein the base layer comprises from about 70 to about 99% by weight ofa propylene polymer.
 43. Method according to claim 42, wherein thepropylene polymer is a propylene homopolymer.
 44. Method according toclaim 9, wherein the base layer is opaque and comprisesvacuole-initiating fillers.
 45. Method according to claim 44, whereinthe base layer also comprises pigments.
 46. Method according to claim44, wherein the opaque base layer comprises one or mare of a) from about0.5 to about 30% by weight of vacuole-initiating fillers and b) fromabout 1 to about 10% by weight of pigments.
 47. Method according toclaim 9, wherein the base layer comprises one or more of lubricants andan antistatic.
 48. Method according to claim 47, wherein the antistaticis a tertiary aliphatic amine.
 49. Method for the production of alabeled container, wherein a biaxially oriented multilayered coextrudedpolyolefin film comprising a base layer and at least oneadhesion-promoting layer, said adhesion-promoting layer comprising (a)at least about 70% by weight of a terpolymer (I) present within saidadhesion-promoting layer alone. said terpolymer built up from (i) olefin(ii) an unsaturated carboxylic acid or ester thereof or an anhydridethereof selected from acrylic acid or methacrylic acid and (iii) anunsaturated monocarboxylic acid ester or an unsaturated dicarboxylicacid or anhydride thereof selected from glycidyl methacrylate, maleicacid or maleic anhydride, and (b) not more than 30% by weight of adeposit preventing additive, wherein the % by weight are in each casebased on the weight of adhesion-promoting layer is applied to acontainer by means of in-mould or thermolabelling methods, and theadhesion-promoting layer faces the container, and the opposite surfaceforms the visible side of the container.
 50. Method according to claim49, wherein no (i) adhesive, (ii) additional bonding layer or (iii)coating is applied to the surface of the adhesion-promoting layer of thepolyolefin film after production of the polyolefin film and beforelabeling of the container.
 51. Method according to claim 49, wherein thecontainer is made from thermoplastic.
 52. Method according to claim 51,wherein the thermoplastic is PP, PE, PS, PVC or PC.
 53. Method accordingto claim 49, wherein the labeling method is thermolabeling, and thelabel is applied to a shaped container with its adhesion-promoting layerat a temperature of above about 50° C., wherein either one or both thecontainer and the label are warned and the label is applied by means ofpressure, rolls or brushes.